Created
October 16, 2013 13:24
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HTML5 Server-Sent Events + Java Servlet example
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| package net.viralpatel.servlets; | |
| import java.io.IOException; | |
| import java.io.PrintWriter; | |
| import javax.servlet.ServletException; | |
| import javax.servlet.http.HttpServlet; | |
| import javax.servlet.http.HttpServletRequest; | |
| import javax.servlet.http.HttpServletResponse; | |
| public class HelloServlet extends HttpServlet { | |
| public void doGet(HttpServletRequest request, HttpServletResponse response) | |
| throws ServletException, IOException { | |
| response.setContentType("text/event-stream"); | |
| response.setCharacterEncoding("UTF-8"); | |
| PrintWriter writer = response.getWriter(); | |
| for (int i = 0; i < 20; i++) { | |
| writer.write("data: "+ System.currentTimeMillis() +"\n\n"); | |
| writer.flush(); | |
| try { | |
| Thread.sleep(1000); | |
| } catch (InterruptedException e) { | |
| e.printStackTrace(); | |
| } | |
| } | |
| writer.close(); | |
| } | |
| } |
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| <!DOCTYPE HTML> | |
| <html> | |
| <head> | |
| <title>Server-Sent Events Servlet example</title> | |
| <style> | |
| body { | |
| font-family: sans-serif; | |
| } | |
| </style> | |
| </head> | |
| <body> | |
| Time: <span id="foo"></span> | |
| <br><br> | |
| <button onclick="start()">Start</button> | |
| <script> | |
| function start() { | |
| var eventSource = new EventSource("HelloServlet"); | |
| eventSource.onmessage = function(event) { | |
| document.getElementById('foo').innerHTML = event.data; | |
| }; | |
| </script> | |
| </body> | |
| </html> |
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| <?xml version="1.0" encoding="UTF-8"?> | |
| <web-app id="WebApp_ID" version="2.4" | |
| xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" | |
| xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd"> | |
| <display-name>ServerSentEvent_HttpServlet_example</display-name> | |
| <welcome-file-list> | |
| <welcome-file>index.jsp</welcome-file> | |
| </welcome-file-list> | |
| <servlet> | |
| <display-name>HelloServlet</display-name> | |
| <servlet-name>HelloServlet</servlet-name> | |
| <servlet-class>net.viralpatel.servlets.HelloServlet</servlet-class> | |
| </servlet> | |
| <servlet-mapping> | |
| <servlet-name>HelloServlet</servlet-name> | |
| <url-pattern>/HelloServlet</url-pattern> | |
| </servlet-mapping> | |
| </web-app> |
After 20 messages, a new eventSource connection has been established. I am unable to find who is establishing this new connection after the writer has been closed in the servlet.
This is due to the fact that the connection on the client side is not closed. The magic of server sent events is that if the connection is closed for whatever reason (unless you do not close it intentionally) the client tries to reconnect to the server after a default time out ( 3 seconds) if you don't call eventSource.close() on the client side.
This just saved me all the time in the world. Thank you!
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After 20 messages, a new eventSource connection has been established. I am unable to find who is establishing this new connection after the writer has been closed in the servlet.